Bear in mind that around that time we got TOS and the films on Blu-ray too. Maybe TPTB didn't want to flood the market with too much Trek product.
Yet they're releasing it concurrently with TNG...
Ten films and three seasons of TOS were released on Blu-Ray to coincide with the 2009 movie.
Two seasons of TNG and two (?) seasons of ENT are being released to coincide with the 2013 movie.
Doesn't look like market saturation to me. It also doesn't look that different in quantity.